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Researchers working on a new type of bomb detector technology have made the rather underwhelming boast that their kit "could soon give bomb-sniffing dogs some serious competition".

“Bomb-sniffing dogs are expensive to train, and they can become tired,” said study co-lead author Ren-Min Ma, one of the boffins who came up with the new gear. “The other thing we see at airports is the use of swabs to check for explosive residue, but those have relatively low-sensitivity and require physical contact. Our technology could lead to a bomb-detecting chip for a handheld device that can detect the tiny-trace vapor in the air of the explosive’s small molecules.”

Ma and his colleagues fashioned their "plasmon sensor" by placing a layer of cadmium sulfide semiconductor on top of a sheet of silver with a layer of magnesium fluoride dielectric in the middle. It seems that even very tiny amounts of explosive nitro-compounds (TNT and related substances such as PETN, a known terrorist favourite) can have detectable effects on such a setup.

“We think that higher electron deficiency of explosives leads to a stronger interaction with the semiconductor sensor,” said Sadao Ota, one of the development team.

We are told:

The engineers put the sensor to the test with various explosives – 2,4-dinitrotoluene (DNT), ammonium nitrate and nitrobenzene – and found that the device successfully detected the airborne chemicals at concentrations of 0.67 parts per billion, 0.4 parts per billion and 7.2 parts per million, respectively. One part per billion would be akin to a blade of grass on a football field.

“PETN has more nitro functional groups and is more electron deficient than the DNT we detected in our experiments, so the sensitivity of our device should be even higher than with DNT,” said Ma.

Ma and his chums would have found it difficult to arrange a test with actual PETN or TNT as these are genuine high explosives, fairly sensitive stuff, and regulations require elaborate and expensive precautions when they are being handled. The comparatively inert substances the researchers did use - none of which are much good as explosives as they stand, though they all can be (and are) made into proper bomb-type stuff by further processing - will have been much easier to obtain.

It's easy to see, in fact, that the research team's expertise doesn't lie in explosives and security as such, or they wouldn't have chosen to lead with the claim of their tech being as good bomb-sniffer dogs. Anyone who has worked in the field knows that explosives dogs are more or less useless as detectors - not really much better than random chance in most circumstances, and wildly prone to false positives - and that their main job is to deter terrorists, make people feel safer, and also perhaps to offer an excuse for searching people.

And, no matter how sensitive your detector is, if the molecules of explosive to be detected are confined inside a container which is not permeable to them (not difficult to arrange in the case of quite large molecules like these), the chance of one drifting off to hit the detector is going to be really very slim indeed. And that's before we even get into the problem of false positives, which is evidently going to be a big one when the detector can pick up agricultural fertilizer (for that is what ammonium nitrate is mainly used as) at 0.4 parts per billion.

So, probably not much of a flyer at the airport, then. But the suggestion that the kit might be some use for finding old landmines is perhaps more credible. Antipersonnel mines are often non-metallic in construction and frequently employ TNT as a main charge. Particularly as they get old, they are likely to leak explosives into the soil around them and the air above it.

So the new plasmon sensors could well be useful: just not, probably, against the tiny, rare problem of terrorists using PETN. The press release should probably have emphasised the huge, serious issue of landmines. ®

Explosive Bootnote

Pentaerythritol tetranitrate (PETN) is a relatively stable explosive but - attractively, to terrorists - still sensitive enough that it doesn't necessarily require a separate detonator. In regular munitions it is used in detonating cord, and as a secondary explosive between detonators and main charges. PETN was used unsuccessfully by the wouldbe airliner shoe bomber Richard Reid and the pants bomber Umar Farouk Abdul Mutallab.

Lewis Page was formerly employed as an armed-forces Explosive Ordnance Disposal (EOD, bomb disposal) operator in support of the UK police.